This invention relates to measurement of plasma parameters in a tokamak. In particular, this invention departs from the prior art by enabling measurement of the dc toroidal electric field E in a tokamak plasma. Using this invention, a brief, deliberate perturbation of hot tokamak electrons produces a transient synchrotron radiation signal, in frequency-time space, and plasma parameters including the dc electric field can be inferred from the radiation response.
The use of synchrotron emission to deduce plasma properties is an established and important technique. Generally, transient synchrotron emission is used for information on the electron temperature; recently there have been attempts to uncover further details of the electron momentum distribution function f. Prior art methods are limited, however, in that deduction of details of the electron distribution function is based on the synchrotron emission from the entire distribution of electrons; consequently, only one-dimensional data (in frequency) can be used to constrain f.
Measurement of the dc parallel electric field has been unavailable using methods of the prior art. Typically less than a volt per meter in a tokamak, this field is far too small to be inferred through atomic phenomena, and cannot be measured directly by probes because the plasma is too hot. Its effect is manifest, however, in the dynamics of superthermal electrons--those that synchrotron radiate most profusely.
It is the primary object of this invention to provide a method for measurement of the dc toroidal electric field E in a tokamak plasma.
In the accomplishment of the foregoing object, it is another important object of this invention to provide a method for inferring other parameters of tokamak plasma from the transient radiation response produced by brief perturbation of the plasma.
It is another important object of this invention to provide a method for distinguishing the steady dc electric field from noise.
It is a further object of this invention to present a method for comparing parameter sets that might possibly explain an incremental transient signal and for estimating the informative worth of the data prior to obtaining it.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.